Projectile hit scorer and detection means

ABSTRACT

Electrical signal-generating target including a conductive layer and a nonconductive barrier ahead of it in the direction from which projectiles arrive to provide a signal having portions of opposite polarity and a target system employing such a target and signal analyzers to determine signal amplitude and duration and the presence of signals of opposite polarity.

United States atet inventors Donald L. Knippel 7 Huntington Beach;

Y. Dairies Lund, Laguna Hills, both of, Calli.

Appl. No. 841,308

Filed July 14, 1969 Patented Aug. 31, 1971 Assignee Babcock Electronics Corporation Costa Mesa, Calif.

PROJECT [LE HIT SCORER AND DETECTXON MEANS 7 Claims, 10 Drawing Figs.

US. Cl 273/1022 R Int. Cl F4lj 5/04 Field of Search 273/l02.2, 102.2 A

[56] v ReierencesCited UNITED STATES PATENTS 3,401,939 9/1968 Mura 273/102.2A

Primary Examiner-Anton O. Oechsle Assistant Examiner-Marvin Siskind Att0rneyNienow & Frater ABSTRACT: Electrical signal-generating target including a conductive layer and a nonconductive barrier ahead of it in the direction from which projectiles arrive to provide a signal having portions of opposite polarity'and a target system employing such a target and signal analyzers to determine signal amplitude and duration and the presence of signals of opposite polarity.

TRlGGER PATENTEU AUGSI I971 3.602.510

SHEET 2 [IF 2 Fig 4 L fi 0 TIME 0 TIME INVENTORS W DONALD L.KN|PPEL J Y. DAINESHLUND ATTOR N EYS PROJECTILE HIT SCORER AND DETECTIQN MEANS This invention relates to improvements in systems for scoring the effectiveness with which projectiles are directed toward a target.

In connection with many kinds of exercises employed in the training of police, security, and military personnel in the use of weapons that fire projectiles and missiles, there is a need to determine immediately whether the projectile has missed its target. A wide variety of sensing devices is available for de tecting whether a target has been struck. There are few sensing devices for making that determination which remain effective after being struck repeatedly by live ammunition.

It is an object of the invention to provide an improved target-hit sensor and target-hit-sensing system and it is an object to provide such a sensor and system which will remain effective and accurate through a greater number of hits than have previously available sensors and systems. Another object of the invention is to provide such a sensor which is easily constructed of inexpensive material. In this connection, it is an object to provide a sensing structure which is capable of sensing hits by projectiles of widely different caliber. ln training exercises designed to approach actual environmental conditions, it is often desirable that a single target be fired on from multiple sources. In this connection, it is an object of the invention to provide a sensor which makes it possible to distinguish a hit from a projectile of one caliber from a hit with a projectile of another caliber and the provision of a sensor and sensing system with this capability is another object of the invention. A related object is to provide a sensor which can distinguish between missiles on the basis of their transit time through the target and the amount of energy dissipated in hitting the target.

Other objects of the invention are to provide a bullet-scoring target and system which provide electrical signals of a kind that may be easily processed for direct readout in the vicinity of the target or that can be telemetered to remote locations. Thus, it is an object of the invention to provide a sensor whose signal form makes it convenient for use inairborne targets as well as for use as a ground-based target.

These, and other objects of the invention which will hereinafter appear, are realized in part by the provision of a target comprising a layer of barrier material capable of decelerating a projectile passing through it and further comprising a layer of conductive material, the layer of barrier material being disposed at the side of the conductivelayer toward the direction from which projectiles approach the target. Also these several objects and advantages and others are realized by the provision of a system incorporating such a target in combination with detection means for detecting signals in the form of potential differences between the conductive layer and a common electrical ground. The barrier layer may be conductive but advantageously is nonconductive.

In the drawings:

FIG. 1 is an isometric view of the several elements of a projectile-scoring system embodying the invention and employing a target embodying the invention;

FIG. 2 is a diagram of a bullet entering a target embodying the invention and an associated measuring apparatus for analyzing the phenomenon occurring at the target;

FIG. 3 is a schematic diagram of a target and target system embodying the invention;

FIG. 4 is a graph of the output signal voltage plotted against time for a target of a given kind;

FIG. 5 is a diagram of a target which will produce a signal like that depicted in FIG. 4;

FIG. 6 is a graph of the signal output voltage plotted against time for a target of another kind;

F IG. 7 is a diagram of a target of a type which will produce an output signal of a kind depicted in FIG. 6;

FIG. 8 is a diagram of an alternative form of target embodying the invention;

FIG. 9 is a graph of the signal voltage output plotted against time which is expected from a target of the type illustrated in FIG. 8; and

FIG. 10 is a graph of the signal output voltage against time which is provided when a hit is scored on another alternative form of target.

Referring to FIG. 1 of the drawings, the system there shown comprises a target 10, electrical output signals from which are conducted by an underground cable 12 to a signal-processing unit 14 whose output is directed by an underground cable 16 to a score-indicator display unit 18. The target 10 provides an output signal when struck, or nearly struck, by a projectile or missile such, for example, as a projectile fired from the gun 20.

A target embodying the invention incorporates at least three structural characteristics. It includes a barrier which will impede the passage of the missile or projectile sufficiently so that it loses a material portion of its kinetic energy. It includes a conductive material in proximity to that barrier, and the point at which the projectile strikes the barrier, so that an electrostatic field is established between that conductor and the projectile, or the barrier in the region of the projectiles impact, of magnitude sufficient to permit measurement. The third structural requirement is that the barrier be placed so that it is struck by the projectile prior to the striking of the conductive material by the projectile. Thus, if the barrier and the conductive material are arranged so that the projectile will strike them both, then the barrier must be placed ahead of the conductive material.

These requirements can be understood by examination of the test system of FIG. 2. In FIG. 2, the target 22 comprises a barrier 24 of nonconductive conductive material. A layer of conductive material 26 lies closely adjacent one face of the layer 24. The target is arranged so that projectiles, such as the projectile 28, will strike the target at its nonconductive side first and will strike the conductive layer of the target after having passed through the nonconductive layer. On the occasion of a projectile striking the target, electrons will be caused to flow into and out of the conductive layer 26 through a load circuit represented by the load resistor 30 to a common ground. The voltage across the load 30 is impressed across an oscilloscope 32 after passage through a suitable filter 34 which filters out signals that are not the result of impingement of the projectile upon the target. The oscilloscope 32 is rendered effective to depict the voltage variation with time by receipt of a signal from a trigger 36 which in this test system responds to an electrical signal generated in an acoustic transducer 38 and applied to the trigger 36. The transducer 38 may have the form of crystal microphone as shown and it can be made responsive to the report from the firearm that propelled the projectile. As shown on the face of the oscilloscope, the signal that is produced comprises a positive, almost square wave, followed by a negative spike whose amplitude is reduced exponentially. The positive pulse results from the striking of the nonconductivebarrier 24 by the missile. The negative spike results from impact of the missile with the conductive layer 26. That part of the wave that is shown in a solid line has already been generated by the projectile partially traversing the layer 24. The dotted line in the oscilloscope display depicts the anticipated portion of the signal that will be generated as the projectile 28 continues on its path through the target. The transition from positive to negative in the signal wave form occurs at the instant that the projectile 28 is centered on the plane of the conductive layer 26. The wave shape is similar when the barrier is formed of conductive material provided, of course, that the barrier is insulated from the conductive layer 26.

If a projectile is tired through an opening in-a conductive plate which is connected to ground through a load resistance or is otherwise arranged so that the flow of electrons to and from the plate can be determined, then electrons will flow through the load resistance into the plate and out of the plate to generate a voltage in the load resistance similar to that de picted in FIG. 10. In that figure the transition from a positive to a negative signal marks the time of passage of the projectile through the opening in the target. Experimentation has resulted in measurement of the wave shape depicted in FIG. 10 as well as of the inverse of that wave shape indicating that as a missile proceeds through the air it can accumulate either a negative or a positive charge although the charge accumulated is most often negative. This phenomenon occurs at projectile velocities sufficientlylow to negate the theory that the charge is developed by ionization of air in the compression wave ahead of the projectile. Given that information and test results showing that a signal of the kind depicted on the oscilloscope 32 of FIG. 2 results upon passage of a projectile through a targetlike target 22 from its barrier side, it is hypothesized that ionization occurs when the projectile strikes the target.

Development of a hypothesis to explain completely the ionization process and target signal generation awaits further test verification and experimentation. Certain barrier materials react with a projectile to provide a target output signal having inverted polarity. Thus while paper, wood, fiberboard and most plastic materials result in generation of a target signal which is positive while the projectile is in the barrier and is negative as it traverses the conductive layer, a barrier of polyethylene foam results in a target signal which is at first negative and then positive.

Except that the polarity must be known in advance whereby the instrumentation may be properly arranged, it makes no difference to effectiveness of the target and system whether the hit signal is first positive or negative. It is very significant that the signal changes polarity and that the amplitude permits convenient measurement of target output signals. Direct current signals are generated and signal amplitude is relatively low. Also, signal processing must usually be done at some distance from the target. The generation of a signal which changes polarity greatly facilitates distinguishing hit signals from noise and rapid drift in ground potentials.

It is clear that electrical charge on the projectile and conductive layer is altered at impact and that the signal output current variation results from electrostatic reaction between the projectile and conductive layer acting as the plates of a capacitor. The separation of those plates changes as the projectile proceeds through the target. One charge being moved relative to another, a voltage wave is generated. The shape of that voltage in time is determined by the motion of the projectile relative to the target. The use of the barrier layer ahead of the conductive layer insures rapid deceleration of the projectile to the end that a large initial pulse (positive or negative) is generated. If the barrier material is uniform the pulse will have a relatively flat top. Pulse amplitude is variable with the amount of energy dissipated in traversing the barrier. Pulse duration is a measure of transit time. Thus, the pulse amplitude and duration are indicative, for a given target, of the energy in a projectile striking it, and permit identification of hits by projectiles of different caliber or, if of the same caliber, of different velocity. This makes it feasible to use a single target to score hits from multiple projectile sources. The amplitude of the spike (usually negative) that follows is determined by the amount of energy lost as the projectile passes through it.

These relationships are illustrated in the several idealized graphs of the drawings. FIG. 4 illustrates the shape of the signal appearing across the load resistor d of FIG. 5 when the target 42 of FIG. 5 is hit and traversed from the left. The voltage rises (positive in this example) when the projectile first strikes the face of the nonconductive layer Ml. It remains approximately constant as it traverses the uniform nonconductive layer and then goes negative as the projectile begins to pass through the conductive layer 46 which in this case overlies the nonconductive layer. Thereafter the negative signal decays to zero.

FIG. 6 illustrates that the positive pulse is omitted if the nonconductive, barrier layer is omitted as in the target 48 of FIG. 7. It is assumed that the projectile enters the target from the left in the figure. The output signal across load 50 goes negative when the projectile enters the target and it decays exponentially thereafter. The addition of a barrier material 52 at the right of conductive layer 54 does not change the shape of the negative going signal but it does increase its amplitude apparently as some direct function of energy lost by the projectile.

The initial pulse occurs prior to the projectiles passing into the conductive layer and this gives rise to the alternative depicted in FIGS. 8 and 9. In FIG. 8 the conductive layer is not continuous but extends over only apart of the target. A projectile passing through a part of the target not covered by a conductive layer might produce the signal depicted in FIG. 9 whereas a projectile passing through that target at a portion where there is a conductive layer would produce a signal like that shown in FIG. 4. The two are distinguishable because the negative spike has much lower amplitude if the projectile passes through the target at a point removed from a portion covered by the conductive layer by a distance several projectile diameters.

Another alternative is illustrated in target of FIG. 3 which is arranged for entry of projectiles from the left through a nonconductive barrier layer 62, into a conductive layer 64 and finally through a layer of stiffening and supporting material 66. Passage of a projectile through this target results in an initial pulse followed by a spike of opposite polarity and of relatively high intensity because of inclusion of the supporting layer 66. The target has a portion 68 which is arranged so that the transit time of a projectile will be longer than when passing through some other portion of the target. The resulting signal output differs in that its pulse duration is longer whereby the signal wave shape makes possible a determination of which portion of the target was struck. In this embodiment the longer transit time is insured by altering barrier thickness, Material could also be varied to alter the impedance to passage at some areas of the target.

In FIG. 3 the conductive layer 64 charges and discharges through a load represented by resistor 70 and which connects from layer 64 to common system ground. Signals appearing across load 70 are amplified in amplifier 72 and appear at the amplifier output at circuit point 74. Some of this signal is applied to a differentiator 76 where they are reduced to positive and negative going spikes. The block diagram assumes that the initial pulse is positive when the target is hit in that the differentiator output is supplied to positive-signal detectors 78 and 80 rather than to negative-signal detectors. The signal to detector 80 is first inverted in an inverter 82. A signal appears at the output of detector 78 in response to the positive pulse at the target and a signal appears at the output of detector 80 in response to a negative spike at the target. The positive output occurs first in time. It is delayed in delay line 84 to coincide with the signal output, if any, from detector 80. Simultaneous occurrence of signals at the output of the detector 80 and delay unit 84 is determined by an AND GATE 86 which permits passage of one of these or another signal to actuate a display means represented by DISPLAY block 88.

Means are provided in the system for determining the duration of the initial pulse and for measuring pulse and spike amplitude. In this embodiment duration is measured by counting at counter 90 the number of pulses emanating from clock 92 while an AND GATE 94, through which the clock pulses pass, is turned on by the initial pulse signal appearing at circuit point M. A rectifier 76 rejects the output signal at point 74 incident to the original target signal spike.

A voltmeter, such as peak voltmeter 98, has its input connected to circuit point 74 to permit measurement of signal pulse and spike amplitudes. A switch selects positive or negative voltmeter input to enable measurement of either portion of the signal.

Although we have shown and described certain specific embodiments of our invention, we are fully aware that many modifications thereof are possible. Our invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

We claim:

1. In a projectile hit scorer;

a. a target comprising a barrier layer of material capable of decelerating a projectile passing through it and further comprising a layer of conductive material, the barrier layer being disposed on the side of the conductive layer toward the direction from which projectiles approach the target;

b. signal-detection means;

c. said conductive layer being provided with a predetermined electrical potential relative to ground during steady-state conditions, the arrangement being such that when a projectile having an electrostatic charge strokes said barrier, the potential difference in said conductive layer is varied to produce a signal detectable by said detection means.

2. The invention defined in claim 1, in which said detection means is effective to detect signals which change polarity.

3. The invention defined in claim 2, in which said detection means comprises polarity-sensitive means for detecting the presence of a negative portion and a positive portion in signals received from said target.

4. The invention defined in claim 3, in which said detection means comprises means for separately detecting positive and negative portions of signals received from the target; and means for superimposing the separately detected signals in time; and an AND GATE responsive to provide an output signal as an incident to simultaneous receipt of said separately detected signals.

5. The invention defined in claim 43, in which the barrier is formed of nonconductive material of a type which results in the generation of a positive potential in the conductive material on the occasion of projectile impact and in which said means for separately detecting positive and negative portions of signals and for superimposing the separately detected signals comprises the parallel combination, between the conductive material and the AND GATE, of a positive-signal detector in series with a time-delay element and an inverter in series with a positive-signal detector.

6. The invention defined in claim 2, which further comprises means for detecting the duration of that portion which has one polarity and is first received of a signal which changes polarity.

7. The invention defined in claim 2, which further comprises means for detecting the amplitude of that portion of a signal which changes polarity and is first received. 

1. In a projectile hit scorer; a. a target comprising a barrier layer of material capable of decelerating a projectile passing through it and further comprising a layer of conductive material, the barrier layer being disposed on the side of the conductive layer toward the direction from which projectiles approach the target; b. signal-detection means; c. said conductive layer being provided with a predetermined electrical potential relative to ground during steady-state conditions, the arrangement being such that when a projectile having an electrostatic charge strokes said barrier, the potential difference in said conductive layer is varied to produce a signal detectable by said detection means.
 2. The invention defined in claim 1, in which said detection means is effective to detect signals which change polarity.
 3. The invention defined in claim 2, in which said detection means comprises polarity-sensitive means for detecting the presence of a negative portion and a positive portion in signals received from said target.
 4. The invention defined in claim 3, in which said detection means comprises means for separately detecting positive and negative portions of signals received from the target; and means for superimposing the separately detected signals in time; and an AND GATE responsive to provide an output signal as an incident to simultaneous receipt of said separately detected signals.
 5. The invention defined in claim 4, in which the barrier is formed of nonconductive material of a type which results in the generation of a positive potential in the conductive material on the occasion of projectile impact and in which said means for separately detecting positive and negative portions of signals and for superimposing the separately detected signals comprises the parallel combination, between the conductive material and the AND GATE, of a positive-signal detector in series with a time-delay element and an inverter in series with a positive-signal detector.
 6. The invention defIned in claim 2, which further comprises means for detecting the duration of that portion which has one polarity and is first received of a signal which changes polarity.
 7. The invention defined in claim 2, which further comprises means for detecting the amplitude of that portion of a signal which changes polarity and is first received. 